A mobile communication system is provided with a transmitting terminal for transmitting through a particular physical channel, and a receiving terminal for receiving through the physical channel. In general, when the physical channel is a reverse link, a mobile station is the transmitting terminal, and a base station is the receiving terminal. Opposite to this, when the physical channel is a forward link, the mobile station is the receiving terminal, and the base station is the transmitting terminal.
In the meantime, the receiving terminal which receives through the physical channel transmits a power control information or instruction called as a power control bit to the transmitting terminal, so that the transmitting terminal controls a transmission power of the physical channel according to the received information.
At least one power control bit (PCB) is transmitted in every power control group period of one frame. The frame is a transmission unit of the physical channel.
For example, referring to FIG. 1, frames each with a 20 ms length are transmitted on the physical channel. each of frame has 16 PCGs with a transmission time period of 1.25 ms. One PCB may be transmitted in one PCG period.
In general, an actual mobile communication environment varies according to time because of negative factors such as fading and interference. Such negative factors vary a quality of the physical channel according to time.
At the end, since the receiving terminal determines a quality of the physical channel presently, the receiving terminal performs a power control according to the quality.
In this instance, a power control rule is determined for the power control bit (PCB) provided from the receiving terminal. Depending on the transmission power control rule a power control rate for controlling the transmission power of the physical channel is determined. In the meantime, for controlling the transmission power of the physical channel, a specific power control rate is set up between the receiving terminal and the transmitting terminal through an initial negotiation. Then, the transmitting terminal or the receiving terminal transmits power control bits according to the negotiated power control rate. For example, if the transmitting terminal and the receiving terminal is set up at an 800 Hz power control rate in the initial negotiation, the receiving terminal transmits the power control bits at the 800 Hz power control rate. If the transmitting terminal and the receiving terminal is set up at a 400 Hz power control rate in the initial negotiation, the receiving terminal transmits the power control bits at the 400 Hz power control rate.
Occasionally, it is needed to change the power control rate. In this case, the receiving terminal is required to inform the transmitting terminal of the power control rate to be changed, so that the transmitting terminal can detect the power control rate and control transmitting power by itself. And it is difficult to perform blind rate detection without power control rate information for detecting a control rate, therefore it is needed to provide an additional supplementary device for performing a more stable detection of the control rate.